Large scale synthesis and delamination of 2D Mo2CTx (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary tra ...

Synthesis and Characterization of 2D Molybdenum Carbide (MXene)

The layered oxides of vanadium and molybdenum have been studied for close to 40 years as possible cathode materials for lithium batteries or electrochromic systems. The highly distorted metal octahedra naturally lead to the formation of a wide range of layer structures, which can intercalate lithium levels exceeding 300 Ah/kg. They have found continuing success in medical devices, such as pacemakers, but many challenges remain in their application in long-lived rechargeable devices. Their high-energy storage capability remains an encouragement to researchers to resolve the stability concerns of vanadium dissolution and the tendency of lithium and vanadium to mix changing the crystal structure on cycling the lithium in and out. Nanomorphologies have enabled higher reactivities to be obtained for both vanadium and molybdenum oxides, and with the latter show promise for electrochromic displays.

Layered vanadium and molybdenum oxides: batteries and electrochromics

We report on the fabrication, the morphological, structural, and chemical characterization, and the study of the electrical response to NO 2 and other gases of resistive type gas sensors based on liquid chemically exfoliated (in N-methyl pyrrolidone, NMP) MoS 2 flakes annealed in air either at 150 °C or at 250 °C. The active material has been analyzed by scanning electron microscopy (SEM), and micro Raman and X-ray core level photoemission spectroscopies. SEM shows that MoS 2 exfoliated flakes are interconnected between electrodes of the sensing device to form percolation paths. Raman spectroscopy of the flakes before annealing demonstrates that the flakes are constituted by crystalline MoS 2 , while, annealing at 250 °C, does not introduce a detectable bulk contamination in the expected form of MoO 3 . The sensor obtained by thermal annealing in air at 150 °C exhibits a peculiar p -type response under exposure to NO 2 . In line with core level spectroscopy evidences, this behavior is potentially ascribed to nitrogen substitutional doping of S vacancies in the MoS 2 surface (nitrogen atoms being likely provided by the intercalated NMP). Thermal annealing the MoS 2 flakes in air at 250 °C irreversibly sets an n -type behavior of the gas sensing device, with a NO 2 detection limit of 20 ppb. This behavior is assigned, in line with core level spectroscopy data, to a significant presence of S vacancies in the MoS 2 annealed flakes and to the surface co-existence of MoO 3 arising from the partial oxidation of the flakes surface. Both p- and n -type sensors have been demonstrated to be sensitive also to relative humidity. The n -type sensor shows good electrical response under H 2 exposure.

Response to NO2 and other gases of resistive chemically exfoliated MoS2-based gas sensors

Colouration of tungsten oxide films: A model for optically active coatings

Gas sensing properties of MoO3 nanorods to CO and CH3OH

Properties of rf‐sputtered molybdenum oxide films for electrochromic display devices have been investigated. This report mainly concerns the dependence of the properties on the oxygen concentration in the sputtering atmosphere. The oxide films were prepared by rf sputtering from a compressed powder MoO3 target under an operating pressure of 4×10−2 Torr using a mixture of Ar‐0.5–50% O2. Electrical resistivity of the films formed increases with increasing oxygen concentration in the sputtering atmosphere and ranges from 2.5×1010 to ∼1×1012 Ω cm. Spectral transmittance of the films is about 85% in the visible and near‐infrared region. Optical band gap and refractive index of these films are 2.67–2.76 eV and 2.01–2.26, respectively. Electrochemichromic properties of the films were also studied using asymmetric cells, and it was found that a good electrochromic performance was obtained usually by the cells composed of the films with a resistivity of 2.5×1010 Ω cm.

S. Akiyoshi

Papers

Preparation and electrochromic properties of rf‐sputtered molybdenum oxide films